The proposed research is designed to investigate the dynamics of iron loading in patients with sickle cell disease and other congenital hemolytic anemias. This will be done by serially quantitating erythrocyte and plasma ferritin by immunoassay and determining its degree of iron saturation. This will be correlated with tissue iron stores when possible. The effects on the dynamics of iron loading of a variety of clinical factors and hypertransfusion in selected patients will be determined.